Modulator arrangement



y 7,1942- N. H. CLOUGH I 2,289,243

MODULATOR ARRANGEMENT 7 Filed June 5, 1940 e6 I 2 I 1 5 naisouecz.

a +HT l /4 A V MODULATION m 5 z POTENTIAL SOURCE 7-,

l4 HIGH DIRECT R-@'?Rmu-cy 9 //CURRENT STAGE SOURCE HT Eb iNVENTOR V NEWSOME H. CL OUGH BY igg/ ATTORNEY Patented July 7, 1942 uul'reo MODULATQPR ARRANGEMENT Newsome Henry Clougli, Brentwood, England, as-

signor to Radio Corporation of America, a cor poratlon of Delaware Application June 5, 1940, Serial No. 338,861

In. Great Britain February 16, 1939 9 6 Claims.

This invention relates to amplifier arrangements and more particularly, though not exclusively, to amplifier arrangements for modulated carrier wave radio transmitters. The invention has for its main object to provide coupling arrangements between so-called sub-modulator and modulator valves.

According to this invention an amplifier arrangement comprises a main modulator stage connected in series with a stage at which modulation is to be effected across a source of potential, a circuit including a direct current permeable impedance in series with a sub-modulator stage being connected across said second mentioned stage, and the junction of said impedance with said sub-modulator stage being connected to the grid of the main modulator stage,

modulating potentials being applied between the grid of the sub-modulator stage and the cathode thereof. i

In describing my invention reference will be made to the attached drawing wherein Figure 1 illustrates a modulation system comprising a main modulator stage, a modulated stage coupled thereto, and a sub-modulator stage connected lustrated in the accompanying drawing, there is employed a main modulator valve Vm having its anode 6 connected to the positive terminal HT+ of a direct current source 9 and its cathode l0 connected to the high potential terminal of a high frequency carrier stage-usually a driven high frequency amplifier-these elements being represented, in general, by the reference R. The

potentials are applied to the grid it of the submodulator valve Vs and through a source B of potential to the cathode of said sub-modulator,

said source of potential having its positive tervoltage and current at which it is operating. If

now the grid, connected to the terminal Tl, of the sub-modulator valve Vs. is made sufliciently negative with respect to the other modulation input terminal T2 to prevent current flow in the sub-modulator valve even at the full value of high tension voltage, there will be no voltage drop across the resistance and the bias on the modulator valve Vm will be removed. If, on the other hand, the grid of the sub-modulator valve Vs is made positive relatively to the previous potential thereof or relatively to T2 by an amount equal to the steady voltage between said cathode and the said other modulation input terminal T2, (i. e. equal to the bias voltage provided by the source B) the sub-modulator bias will, in effect, be removed. In consequence the increased current through the resistance Rb will apply more bias to the modulator valve, and this will reduce the current passed by the modulator valve Vm, in turn reducing the voltage applied to the submodulator valve and preventing any great increase in current through the said resistance Rb. By suitable selection of the values of the said resistance Rb and of the auxiliary source Eb between the cathode of the sub-modulator valve and earth, it is possible to arrange for the voltage across the said resistance Rb, i. e. the modulator valve bias, in the condition mentioned, to approach cut-off. The two conditions, one where the grid of the sub-modulator valve V; is negative and the other where the said grid is positive, both with respect to the said other modulation input terminal, correspond respectively to the peak and trough of deep modulation. Where less deep modulation is required, the auxiliary source Eb between the cathode of the submodulator valve and earth, might be omitted.

- An advantage of the invention is that the coupling between the sub-modulator and modulator valves is substantially purely resistive, and the circuit, therefore, is suitable not only for cases where sinusoidal inputs and outputs are in question, but also in cases where non-sinusoidal wave forms arise, e. g. for telegraph systems or for television systems.

In order to increase the upward swing of modulation it may be desirable, in some cases, to include a source of potential between the resitsance Rb and the cathode of the modulator valve Vm, the negative end of said source being towards said cathode. This arrangement has been shown in Figure lo. I In practice this source of potential might take the form of a rectifier and filter circuit receiving input from an extra winding on a transformer normally employed for heating the filament or cathode of the modulator valve.

Alternatively in cases where direct current amplification is not involved, a check 26 may be substituted for the submodulator anode resistance Rb, bias for the modulator valve being provided by a capacity shunted resistance Rb on the positive side of the choke as shown in Figure 1b. Where 100% modulation is required the choke may be extended beyond the sub-modulator anode, i. e. the said anode may be connected to a tap on the choke as shown in Figure lb, or, instead of this tapped choke arrangementwhich is, in effect, an auto-transformer arrangement, a double wound transformer 30 may be used as shown in Figure 10, to reduce magnetic leakage.

Although the main application of the invention is to radio and like transmitters, and it has been particularly described as so applied, the invention is applicable toamplifier arrangements generally; for example, the high frequency stage hereinbefore referred to might be replaced by the resistance of a loudspeaker or an audio frequency load of any sort in cases in which it was required to amplify audio frequency.

What is claimed is:

1. In an amplifier system, two electron discharge devices each having an anode, a cathode and a control electrode, a source of direct current potential, a load circuit connected in series with the internal anode-cathode impedance of one of said devices, means coupling said series arrangement of load circuit and internal device impedance across said source of direct current potential, the anode of said one device being connected to the positive terminal of said direct current source, said load circuit being between the cathode of said one device and the negative terminal of said direct current source, an impedance connected to the anode of said other device and in series with the internal anode-cathode impedance of the other device, connections connecting said last series arrangement of said last named impedance and the internal impedance of said other device in shunt to said load circuit, a substantially direct connection between the anode of said other device and the grid of said one device, and means for impressing voltages to be amplified on the grid and cathode of said other device.

2. In 'a modulation system, two electron discharge devices each having an anode, a cathode and a control electrode, a high frequency stage wherein high frequency energy to be modulated is set up and a source of direct current connected in series with the internal anode-cathode impedance of one of said devices, the positive terminal of said source of direct current being connected to the anode of said one device, said high frequency stage being connected between the cathode of said one of said devices and the negative terminal of said source of direct current, an impedance connected to the anode of the other device and in series with the internal anode-cathode impedance of said other device, connections connecting said last series arrangement of said impedance and said internal anodecathode impedance of said other device in shunt to said high frequency stage, a substantially direct connection between the anode of said other device and the grid of said one device, and means for impressing modulating voltages on the grid and cathode of said other device.

3. A system as recited in claim 1, wherein a source of direct current potential is included in said connections connecting said last series arrangement of impedance and internal tube impedance in shunt to said load circuit.

4. In a modulation system, two electron discharge devices each having an anode, a cathode and a control electrode, a radio frequency stage and a source of direct current connected in series with the internal anode-cathode impedance of one of said devices, the positive terminal of said source of direct current being connected to the anode of said one device, said radio frequency stage being connected between the cathode of said one device and the negative terminal of said source of direct current, an impedance connecting the anode of the other device to the cathode of said one device, a source of direct current potential connecting the cathode of the other device to said radio frequency stage at its point of connection to the negative terminal of said direct current source, a connection between the anode of said other device and the grid of said one device, and means for impressing modulating potentials on the grid and cathode of said other device.

5. A system as recited in claim 4 wherein said impedance connecting the anode of said other device to the cathode of said one device is shunted by a condenser and wherein said con-' nection between the anode of said other device and the grid of said one device includes an inductance.

6. A system as recited in claim 4 wherein said impedance connecting the anode of the other device to the cathode of said one device is shunted by a condenser and wherein said connection between the anode of said other device and the grid of said one device includes a transformer.

NEWSOlifli HENRY CLOUGH. 

